This invention relates to improved dentifrice formulations. In particular, it involves the use of pH-modified synthetic and/or natural zeolites as multifunctional components for dentifrices.
In the United States alone, estimates place the cost of repairing the effects of tooth decay at six billion dollars annually. The first line of defense is the individual's own dental hygiene program. For each person, this primarily involves daily use of a dentifrice to clean the teeth. Modern dental research has shown that decay results from localized demineralization of tooth enamel. This demineralization is caused by the action of acids which are formed by specific bacteria metabolizing fermentable carbohydrates. These bacteria are found adhering to the plaque which forms on the teeth, often comprising as much as 70% of the plaque itself. Further studies have shown that demineralization takes place at a pH of 5.5 or less. Above pH 6 demineralization ceases. (H. J. Sanders; Chemical and Engineering News, Feb. 25, 1980.)
Therefore, a proper dentifrice formulation used to clean the teeth, sweeten breath, and reduce tooth decay must do the following:
a. Keep the pH at 6 or above--the non-demineralization zone; and PA1 b. Remove the plaque which serves as a situs for the specific bacteria whose metabolic action is the prime cause of tooth decay.
Additionally, since the dentifrice is for human use, it must be biologically compatible and safe for repeated use.
Besides the above objective criteria, dentifrices must be esthetically acceptable to the persons who will use them. Taste and texture must be pleasing and the dentifrice must not produce any unpleasant sensory perceptions. Organoleptic testing has shown that despite objective usefulness of a dentifrice, it will be rejected if its psycho-sensory effects are objectionable.
Modern dentifrice compositions contain numerous components that have various therapeutic and cosmetic functions. Most of these compositions contain some sort of abrasive cleansing agent which aids in the removal of adherent deposits on the teeth. Particulate matter of specific hardness and certain particle size, shape and structure is utilized as such abrasives. These particles must also be compatible with other toothpaste ingredients and safe for repeated human use. Abrasives that are described in the patent literature and have found commercial application include silica xerogels, hydrated silicas, hydrated aluminas, calcium carbonate, dicalcium phosphate (anhydrous and dihydrate), calcium pyrophosphate and insoluble sodium metaphosphate. These agents are usually 2 to 30 .mu.m in size. Products of about 10 .mu.m appear to find the most commercial acceptance. Insoluble crystalline materials such as quartz have been found too abrasive for safe use on human dentition.
Many dentifrice formulations contain a polishing or lustering agent in addition to the abrasive. These materials are generally softer and of smaller particle size than the abrasives. These agents are not useful in removing adherent stains and other material from the teeth; instead, they provide so-called luster to the teeth by a fine polishing action. Some of the agents used in this capacity include diatomaceous earth, pyrogenic and aerogel silicas and amorphous alumino-silicates. U.S. Pat. Nos. 3,911,104 and 4,036,949 disclose the use of amorphous alumino-silicates for such polishing agents. These materials have very high silica-to-alumina ratios and are not considered abrasives.
A desirable ingredient for dentifrices is one that provides both abrasive and polishing actions. Such a dual-purpose material greatly simplifies the formulation and production of these multi-component products. Most abrasive particles must be .about.10 .mu.m or more in size to provide adequate action while particles of less than about 1 .mu.m are required for polishing action. Producing particulate products with such bi-modal or wide range particle size distribution is difficult, expensive and is not done. Some silicas suggested as abrasives are crushed during use to provide particles of the correct size for polishing. The materials that provide sufficient crushed particles for good polishing often exhibit poor abrasion.
Additional siliceous or similar materials are required to thicken toothpastes as well as provide carriers for many additional ingredients.
Zeolites have been suggested as components in toothpastes and powders. Frank (German Empire Patentschrift 378010) suggested the use of what he called the base exchanging property of zeolites to aid in the dissolution of scale. He pointed out that a toothpaste using fine zeolitic powder had a pronounced effect on scale. Menkart and Ricciuti suggested (U.S. Pat. No. 3,250,680) the use of anhydrous zeolites in cosmetic preparations to produce a pleasant warm sensation on hydration during use. Their purpose was an esthetic satisfaction, rather than an objective use. Harth and Becker (U.S. Pat. No. 4,209,504) suggest the use of zeolites as a polishing agent in toothpaste. The main thrust of their invention is the use of zeolite as an agent with no corrosive effect on unlacquered aluminum surfaces. None of these inventions suggested the use of zeolite as an aid in control of dental caries.
Kato et al. (K. Kato, M. Shiba, Y. Okamoto, N. Nagata; Reports of the Institute for Medical and Dental Engineering I, 85: 1973) pointed out the compatibility of zeolites with fluoride ion, which is used as a caries preventive.
None of the above suggestions or inventions point to the use of zeolite, natural or synthetic, as a caries preventive in itself, or allude to the possibility of modifying the zeolite so that it can serve in this function. In addition, there are no commercially available dentifrices which contain zeolite (45 FR 20666-20691).
Most commercially available dentifrices have pH's below the demineralization thresold. For example, the following table gives pH values for the commonly used abrasives in stannous fluoride dentifrices (45 FR 20681).
TABLE I ______________________________________ Hydrogen Ion Concentration (pH) Maximum Test Abrasive Test Value Dilution (w/w) ______________________________________ Insoluble sodium 4.2-5.4 1:10 metaphosphate Silica 4.6-5.1 1:10 Calcium pyrophosphate 4.4-5.1 1:10 ______________________________________
The above pH's are well within the range at which demineralization occurs. It would be advantageous to have a formulation outside of the demineralization range which is still acceptable psychosensorily to the persons who will use it.
It is the prime objective of this invention to have the component zeolite impart a pH of 6 or above to the formulation, but below the pH level at which there is personal objection to the taste and sense of dehydration in the mouth. Also, there is no offensive texture. It is an additional object of this invention, simultaneously with provision for aiding in caries control, to provide zeolites, natural and/or synthetic, as a multifunctional component in dentifrices, providing as well polishing and lustering action and abrasion of plaque, thereby simplifying formulation and manufacture of such compositions.